Definition: Twins with birth weight discordance of more than 20%, calculated from the weight of the larger twin1. Cutoffs for discordance remain controversial between investigators, although most of them have settled on 15%, 20%, or 25% difference in birth weights[1] [2] [3] , [4] , [5] , [6] ,7,8 with clinical correlates to support all three4,6,9,10. In our definition we use the 20% cutoff because it is the most acceptable compromise11,12,13,14,